OpenWrt 18.06 RC2 Dmesg message (urandom, lack of entropy)

Lack of entropy is a real problem in embedded devices right after boot.

I think that the warning for urandom quality was added to the kernel some time ago, but the warning was modified just a few months ago: and backport to 4.9:

You might read Randomness quality for some background on lack of entropy in Openwrt. I wrote there a brief summary of mitigation attempts in Openwrt in the last 5-6 years.